The invention relates to a method for determining a virtual tool centerpoint in reference to a known coordinate system of a robot that has a measuring sensor for measuring objects, and a corresponding control device.
Virtual tool centerpoints (TCPs) refer to spatial coordinates and orientations that lie for example outside of real bodies such as a tool. Such points are located freely in space, and because they lack any reference to real bodies a robot cannot move to them directly. In laser processing by robot, for example, a virtual TCP lies in the focus of the laser; that is, it is located freely in space and not at a geometric point on a real body. Light section sensors are used for example by preference for readjusting during laser processing.
Light section sensors are employed to register surfaces by means of static triangulation. Here a semiconductor laser uses a linear optic unit such as a cylinder lens to produce a flat-fanned laser beam in the form of a light curtain, which strikes an object of measurement and is reflected at the so-called triangulation angle to a camera with signal processing, such as a CCD array. A signal processor analyses the laser lines reflected from the object of measurement to determine the spatial position of the object and any edge transitions. The light section sensor can thereby provide interval measurements and profile sections of the measured object.
Before the values provided by the light section sensor can be used to control a robot or to correct its robot program or for a machine in general, the measured values initially provided by the light section sensor must be made available to the robot in the latter's robot coordinate system, or else in the world coordinate system that is related to the latter in a known way. In so doing, a virtual sensor tool center point—sensor TCP—is defined, whose position is defined in the sensor coordinate system.
In particular after detaching the light section sensor and re-attaching it to the robot arm, for example after the failure of a sensor, and/or in more general terms when the attachment position is not clearly defined, the location of the sensor TCP relative to the robot coordinate system or world coordinate system has usually shifted. This shift is not known at first, and according to the invention is to be determined by simple means.